The present invention generally relates to ablative heat shields for atmospheric entry or re-entry and, in particular, to carbon phenolic ablative compositions for use with such heat shields.
Ablator materials (e.g., carbon phenolic-based ablators, such as phenolic impregnated carbon ablator (PICA)), are often used as the thermal protection system in the fabrication of aeroshells of space vehicle re-entry systems. Such aeroshells have been fabricated by bonding multiple tiles of these carbon phenolic ablators onto a substrate structure, and then filling the gaps between these tiles with room temperature vulcanizing type materials such as RTV silicone. During the gap filling process, a part of the RTV silicone has the tendency to penetrate into the porosity of adjacent tiles. One issue with these RTV silicone-type materials is that they exhibit a very high coefficient of thermal expansion when compared to the ablative tile materials the gaps between which they are used to fill. Therefore, during heating (e.g., during re-entry and thermal soakback conditions), the expansion and contraction of the gap filler material, particularly where it has bonded with adjacent tiles, can trigger the dislodging or chipping of the adjacent tiles, negatively impacting the smooth outer surface (and thereby the performance) of the ablative heat shield material.